Railway cars with an enclosed rectangular cargo space for shipping goods; also, the dice roll of two sixes in craps.
From 'box' (the enclosed shape) and 'car' (railway car). The term emerged in the 1800s. The dice meaning (two sixes = 12) comes from their appearance resembling boxcar wheels.
The lucky dice roll called 'boxcars' might be named because the two dots on each die visually resemble the wheels on the ends of railway boxcars—a perfect example of folk etymology creating vivid language!
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